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Abstract:
In both speech and music, the perceived pitch of a sound can
correspond to a frequency which is not physically present in the
stimulus signal, called the 'missing fundamental' (MF). This
percept is derived from harmonic partials via central neural
processing. Neuropsychological research on patients with
temporal-lobe excisions suggests a special role of the right
hemisphere in extracting the MF, but there is little or no imaging
evidence from normal subjects for the neural lateralization of this
process. We sought a dynamic neural correlate of the missing
fundamental in stimulus-related cortical activity measured with
whole-head magnetoencephalography (MEG). We used amplitude
modulation of pure tones and complex tones (tones with 3 sine-wave
partials at 2x, 3x, and 4x the MF) to generate stimulus-related
cortical activity (the auditory steady-state response, aSSR). We
examined temporal properties of this activity as a function of the
perceived pitch of the stimulus. We have previously shown that the
timing of the aSSR reflects the frequency of pure tone stimuli. The
majority of subjects who heard the MF showed an effect of perceived
pitch on the timing of the aSSR at MEG sensors over the right
anterior hemisphere, an effect not seen in subjects who did not
hear the MF. This provides evidence for lateralization of missing
fundamental pitch extraction in normal subjects. This work was
supported by Neurosciences Research Foundation.
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